The inventive concepts described herein relate to an MEMS microphone, and more particularly, relate to an MEMS microphone including a noise filter.
An MEMS microphone may include a microphone sensor and an MEMS microphone ASIC. A voltage booster in the ASIC may be supplied with a DC reference voltage, and may generate a sensor bias voltage by pumping the DC reference voltage using a charge pump. The charge pump may have a switched capacitor structure, in general. Thus, a noise included in the DC reference voltage may be also included in the sensor bias voltage. In this case, the microphone sensor may be affected directly by the noise included in the DC reference voltage.
A bias circuit included in the ASIC may be supplied with a reference current to generate a bias voltage of an amplifier. A differential amplifier can remove a bias noise. However, an amplifier of the MEMS microphone ASIC may not remove a noise due to impedance mismatching between a source follower and an input terminal. Thus, a noise included in the reference current may affect an output of the MEMS microphone.
A noise of a reference voltage/current generator may include a flicker noise and a thermal noise of a transistor. In general, the flicker noise may be reduced using a large-sized transistor, and the thermal noise may be reduced by increasing transconductance. However, since a size of a circuit implemented using the above-described methods is large, it is difficult to provide a small-sized MEMS microphone. Thus, there may be required a small-sized circuit capable of reducing a noise of a DC reference voltage and a noise of a reference current.